Selection for resistance to a nucleopolyhedrosis virus in laboratory populations of the cotton bollworm, Heliothis zea

Resistance to a nucleopolyhedrosis virus (Baculovirus heliothis) did not develop in laboratory populations of the cotton bollworm, Heliothis zea. A selection pressure of LD₅₀ to 70 was maintained throughout 20 to 25 generations of selection. No significant changes in LD₅₀, slope, or intercept of dose-mortality lines were detected. Laboratory populations under selection were as susceptible to the virus as nonselected or wild populations of H. zea. The resistance ratio (LD₅₀ of selected generation/initial generation) ranged from 0.5 to 1.2.     

Genetic Control of Resistance to the Sterol 14α-Demethylase Inhibitor Fungicide Prochloraz in the Cereal Eyespot Pathogen Tapesia yallundae

Sexual crosses were used to determine the genetic basis of resistance to the sterol 14 α-demethylase inhibitor fungicide prochloraz in the cereal eyespot pathogen Tapesia yallundae. Three different crosses between sensitive parental strains (22-432 and 22-433 [the concentration required to inhibit growth by 50% {IG₅₀} for each was ≤0.03 mg/liter]) and field isolates from France and New Zealand with differing levels of resistance (PR11 [IG₅₀ = 0.5 mg/liter], PR1 [IG₅₀ = 1.0 mg/liter], and 11-3-18 [IG₅₀ = 2.4 mg/liter]) yielded progeny showing a bimodal distribution, with an even number of sensitive and resistant progeny. This indicated the segregation of a single major gene for resistance in each cross, which was confirmed by the use of backcrosses, crosses between F₁ progeny, and control crosses between sensitive parents. However, there was also evidence of additional quantitative genetic components responsible for the increased IG₅₀s of the more resistant isolates. A further cross was made between isolate PR11 and an F₁ progeny arising from isolate 11-3-18, and this also yielded progeny which were entirely prochloraz resistant. This suggested that resistance genes were allelic in these two isolates, with resistance conferred by a gene at the same locus (or closely linked loci), despite the fact that the isolates (PR11 and 11-3-18) originated from different continents.     

Susceptibility of Heliothis armiger to a commercial nuclear polyhedrosis virus

The susceptibility of Heliothis armiger larvae of different ages to a commercial nuclear polyhedrosis virus (NPV), Elcar, was determined by bioassay. The median lethal dosage (LD₅₀) increased 150-fold during the first week of larval life at 25°C, i.e., during development to early fourth instar, but daily feeding rate and thus potential virus acquisition also increased. A linear relationship was determined between log LD₅₀ and larval length, indicating that larval length constitutes a useful index for estimating the susceptibility of larval populations. Median lethal times (LT₅₀s) were similar for larvae tested at ages of 0 to 7 days and ranged from 3.6 to 8.0 days at 30°C. The amount of virus produced in a single, infected neonate was equivalent to 1.4 × 10⁶ LD₅₀s for neonates, a 900,000-fold increase on the dose supplied. The data support the practice of directing the NPV against neonates, but, on the basis of larval susceptibility alone, the age of larvae at treatment may not always be critical.     

棉铃虫对氰戊菊酯抗性和敏感品系的选育

用氰戊菊酯对来自阳谷的棉铃虫(YG)Heliothis armigera(Hubncr) 进行抗性晶系的筛选。在15代期间经过9代的室内选育,获得抗性品系(Fcn-R),抗性倍数高达2“3倍,筛选后F₁₅代LD₅₀值(24.1412μg/头)比筛选前F1代lD₅₀值(0.2020μg/头)提高了119.5倍。对来自偃师的棉铃虫(YS)进行了连续两代单对筛选,得到敏感品系(Fen-S),敏感晶系的LD50值为0.0116μg/头,接近1983年东台敏感晶系的LD₅₀值(0.0098μg/头)Fcn-R抗性晶系筛选前后分别测定了七种杀虫剂的剂量-死亡回归线,发现Fen-R抗性品系对溴氰菊酯[LD₅₀(Fen-R)/LD₅₀(YG)=5.2X] 和氯氰菊酯(2.5X)具有一定程度的交互抗性;而对功夫菊酯(0.66X),氯菊酯(0.89x)、灭多威(0.74X)及久效磷(1.5x)没有交互抗性。氰戊菊酯加Pb的增效试验结果表明棉铃虫对氰戊菊酯的抗性主要是由于多功能氧化酶的代谢作用。毒理学资料还暗示抗性为多因子(基因)的。     

Molecular mapping of leaf rust resistance gene LrNJ97 in Chinese wheat line Neijiang 977671

Neijiang 977671 and 19 near-isogenic lines with known leaf rust resistance genes were inoculated with 12 pathotypes of Puccinia triticina for postulation of leaf rust resistance genes effective at the seedling stage. The reaction pattern of Neijiang 977671 differed from those of the lines with known leaf rust resistance genes used in the test, indicating that Neijiang 977671 may carry a new leaf rust resistance gene(s). With the objective of identifying and mapping the new gene for resistance to leaf rust, F₁ and F₂ plants, and F_2:3 families, from Neijiang 977671 × Zhengzhou 5389 (susceptible) were inoculated with Chinese P. triticina pathotype FHNQ in the greenhouse. Results from the F₂ and F_2:3 populations indicated that a single dominant gene, temporarily designated LrNJ97, conferred resistance. In order to identify other possible genes in Neijiang 977671 other eight P. triticina pathotypes avirulent on Neijiang 977671 were used to inoculate 25 F_2:3 families. The results showed that at least three leaf rust resistance genes were deduced in Neijiang 977671. Bulked segregant analysis was performed on equal amounts of genomic DNA from 20 resistant and 20 susceptible F₂ plants. SSR markers polymorphic between the resistant and susceptible bulks were used to analyze the F_2:3 families. LrNJ97 was linked to five SSR loci on chromosome 2BL. The two closest flanking SSR loci were Xwmc317 and Xbarc159 at genetic distances of 4.2 and 2.2 cM, respectively. At present two designated genes (Lr50 and Lr58) are located on chromosome 2BL. In the seedling tests, the reaction pattern of LrNJ97 was different from that of Lr50. Lr50 and Lr58 were derived from T. armeniacum and Ae. triuncialis, respectively, whereas according to the pedigree of Neijiang 977671 LrNJ97 is from common wheat. Although seeds of lines with Lr58 were not available, it was concluded that LrNJ97 is likely to be a new leaf rust resistance gene.     

Identification and confirmation of quantitative trait loci controlling resistance to mungbean yellow mosaic disease in mungbean [Vigna radiata (L.) Wilczek]

Mungbean yellow mosaic India virus (MYMIV) is a major constraint on mungbean production in South and Southeast Asia. The virus belongs to the genus Begomovirus, causing yellow mosaic disease and subsequently yield loss up to 75–100 %. The present study employed F₂ and BC₁F₁ populations derived from a cross between susceptible (BARImung 1; BM1) and resistant (BARImung 6; BM6) mungbeans to identify quantitative trait loci (QTLs) associated with resistance to MYMIV. Resistance to the virus was evaluated using F_2:3 and BC₁F_1:2 populations under field conditions in two locations in Bangladesh in 2012. A total of 1,165 simple sequence repeat markers from different legumes were used to detect the polymorphism between BM1 and BM6. Sixty-one polymorphic markers were used to construct a linkage map comprising 11 linkage groups. Composite interval mapping consistently identified two major QTLs, qMYMIV2 on linkage group 2 and qMYMIV7 on linkage group 7, conferring the resistance in both F₂ and BC₁F₁ populations. qMYMIV2 and qMYMIV7 accounted for 31.42–37.60 and 29.07–47.36 %, respectively, of the disease score variation, depending on populations and locations. At both loci, the resistant alleles were contributed by the parent BM6. qMYMIV2 appeared to be common to a major QTL for MYMIV resistance in mungbean reported previously, while qMYMIV7 is a new QTL for the resistance. The markers linked to the QTLs in this study are useful in marker-assisted breeding for development of mungbean varieties resistant to MYMIV.     

Genetic analysis of resistance to six virus diseases in a multiple virus-resistant maize inbred line

Key message

Novel and previously known resistance loci for six phylogenetically diverse viruses were tightly clustered on chromosomes 2, 3, 6 and 10 in the multiply virus-resistant maize inbred line, Oh1VI.

Abstract

Virus diseases in maize can cause severe yield reductions that threaten crop production and food supplies in some regions of the world. Genetic resistance to different viruses has been characterized in maize populations in diverse environments using different screening techniques, and resistance loci have been mapped to all maize chromosomes. The maize inbred line, Oh1VI, is resistant to at least ten viruses, including viruses in five different families. To determine the genes and inheritance mechanisms responsible for the multiple virus resistance in this line, F₁ hybrids, F₂ progeny and a recombinant inbred line (RIL) population derived from a cross of Oh1VI and the virus-susceptible inbred line Oh28 were evaluated. Progeny were screened for their responses to Maize dwarf mosaic virus, Sugarcane mosaic virus, Wheat streak mosaic virus, Maize chlorotic dwarf virus, Maize fine streak virus, and Maize mosaic virus. Depending on the virus, dominant, recessive, or additive gene effects were responsible for the resistance observed in F₁ plants. One to three gene models explained the observed segregation of resistance in the F₂ generation for all six viruses. Composite interval mapping in the RIL population identified 17 resistance QTLs associated with the six viruses. Of these, 15 were clustered in specific regions of chr. 2, 3, 6, and 10. It is unknown whether these QTL clusters contain single or multiple virus resistance genes, but the coupling phase linkage of genes conferring resistance to multiple virus diseases in this population could facilitate breeding efforts to develop multi-virus resistant crops.     

Isolation and characterization of a granulosis virus from the tomato moth,Lacanobia oleracea,and its potential as a control agent

A disease causing death in Lacanobia oleracea (Lepidoptera: Noctuidae) occurring in glasshouses in Scotland was shown to be caused by a granulosis virus (GV). Structural properties of the virus were examined by electron microscopy, immunodiffusion, polyacrylamide gel electrophoresis, and restriction endonuclease analysis and compared with an isolate of GV from L. oleracea obtained from France. The two isolates were structurally very similar but could be distinguished by analysis of EcoRI digests of their DNAs. Bioassays of the virus gave LD₅₀ values from 10^4.3 capsules for second-instar larvae to 10^6.6 capsules for fifth-instar larvae. The French isolate was bioassayed in third-instar larvae and was not found to differ significantlyfrom the Scottish isolate. Two small glasshouse trials using the virus to control artificial infestations of L. oleracea indicated that high-volume sprays of virus at 10⁸ to 10⁹ capsules/ml achieved good control. An alternative strategy using much smaller amounts of virus to control the insect is discussed.     

Putative Thinopyrum intermedium-derived stripe rust resistance gene Yr50 maps on wheat chromosome arm 4BL

Stripe rust-resistant wheat introgression line CH223 was developed by crossing the resistant partial amphiploid TAI7047 derived from Thinopyrum intermedium with susceptible cultivars. The resistance is effective against all the existing Chinese stripe rust races, including the most widely virulent and predominant pathotypes CYR32 and CYR33. Cytological analyses using GISH detected no chromosomal segments from Th. intermedium. It was presumed that the segment was too small to be detected. Normal bivalent pairing at meiosis in CH223 and its hybrids confirmed its stability. Genetic analysis of the F₁, F₂, F₃ and BC₁ populations from crosses of CH223 with susceptible lines indicated that resistance was controlled by a single dominant gene. The resistance gene was mapped using an F_2:3 population from Taichung 29/CH223. The gene was linked to five co-dominant genomic SSR markers, Xgwm540, Xbarc1096, Xwmc47, Xwmc310 and Xgpw7272, and flanked by Xbarc1096 and Xwmc47 at 8.0 and 7.2 cM, respectively. Using the Chinese Spring nulli-tetrasomic and ditelosomic lines, the polymorphic markers and the resistance gene were assigned to chromosome arm 4BL. As no permanently named stripe rust resistance genes had been assigned to chromosome 4BL, this new resistance gene is designated Yr50. The gene, together with the identified closely linked markers, could be used in marker-assisted selection to combine two or more resistance genes in a single genotype.     

Understanding the inheritance of mungbean yellow mosaic virus (MYMV) resistance in mungbean (<Emphasis Type="Italic">Vigna radiata</Emphasis> L. Wilczek)

Mungbean, Vigna radiata, third in the series of important pulse crops, still suffers from yield loss due to mungbean yellow mosaic disease caused by mungbean yellow mosaic virus (MYMV). Hence, studies on plant-microbe interaction are necessary for understanding the inheritance of resistance. This study concentrated on identification of linked molecular markers for MYMV resistance and to find the genetic inheritance of MYMV resistance in mungbean. A total of 413 germplasm entries in a MYMV hot spot area (Vamban) were subjected to natural field infection and 13 selected resistant lines were subjected to Agrobacterium infection using strains harboring partial genome of two different MYMV isolates, VA221 and VA239. Among the resistant lines, KMG189 showed strain-specific resistance to VA221 and had no symptoms during field trials. Ninety F₂ genotypes were developed from the cross made between KMG189 (MYMV-resistant) and VBN(Gg)2 (MYMV-susceptible), segregated in the Mendelian single cross ratio 3S:1R; susceptibility of all the F₁s to MYMV suggested that the MYMV resistance in mungbean is governed by a single recessive gene. Two SCAR markers CM9 and CM815 were developed through bulk segregant analysis, and the linkage analysis proved CM815 SCAR marker to be linked at 5.56 cM with MYMV resistance gene and SCAR CM9 had nil recombination percentage, suggesting it to be very closely linked to the MYMV resistance gene. SCAR marker CM9 was present in chromosome number 3 of mungbean suggesting novel loci for virus resistance in mungbean. The identified loci can be used for developing varieties resistant to MYMV in mungbean.     

Susceptibility of Hyphantria cunea to a granulosis virus isolated from Diacrisia virginica

The dosage-mortality response of Hyphantria cunea larvae to a granulosis virus isolated from Diacrisia virginica was studied. Serial decimal dilutions of the D. virginica granulosis virus were fed to early second-instar H. cunea larvae. the LD₅₀ for this virus (7.9 × 10⁵ capsules/larva) was significantly greater than the LD₅₀ calculated for the H. cunea granulosis virus (7.06 × 10⁴ capsules/larva) against the same instar of H. cunea. Time mortality studies demonstrated that the LT₅₀ values for the D. virginica granulosis were four to six times greater than for comparable dosages of H. cunea granulosis virus. Based on the mortality response of assayed H. cunea, it is possible to distinguish between the D. virginica granulosis virus and the H. cunea granulosis virus.     

Freeze-Drying of Foot-and-Mouth Disease Virus and Storage Stability of the Infectivity of Dried Virus at 4 C

Foot-and-mouth disease virus, type A, strain 119, propagated in cultures of calf kidney cells and in the tongue epithelium of cattle was used. The process of freeze-drying was conducted in two cycles on unit volumes of 4 ml in Pyrex ampoules, averaging 150 ampoules per run, and was studied separately from the problems of storage. Ampoules containing freeze-dried virus were flame-sealed for either immediate study or storage at 4 C for later reference. Tissue-culture virus dried with various additives had a mean processing loss of 0.8 log LD₅₀ per ml for six different preparations. Virus freeze-dried in tissue suspension had a mean loss of 0.8 log LD₅₀ per ml for three different preparations. A second set of preparations was processed and specifically studied for storage quality at 4 C. The virus in 14 freeze-dried tissue-culture preparations had a mean loss of 0.75 log LD₅₀ per ml while stored at 4 C for 1 year. Virus in four freeze-dried tissue suspensions had a mean loss of 0.05 log LD₅₀ per ml held at 4 C for 1 year. None of the specific additives used for conservation of the virus during the freeze-drying process or during storage at 4 C contributed significantly to the stability of the virus preparations over and above that observed with the normal growth medium of the tissue culture or the ordinary diluents used in making suspensions of tissue virus.     

Biological Comparison of Two Genotypes of Helicoverpa armigera Single-Nucleocapsid Nucleopolyhedrovirus

Baculovirus isolates from the same host species often show a considerable degree of variation on phenotypes. The completely sequenced genotypes C1 and G4 of Helicoverpa armigera single-nucleocapsid nucleopolyhedrovirus (HaSNPV) were compared. Bioassay studies suggested that nearly double of HaSNPV G4 virus was required compared with HaSNPV C1 to achieve a similar LD₅₀, and at the LD₉₀ level the insect-killing speed for HaSNPV C1 was quicker than that of HaSNPV G4. The budded virus (BV) production of HaSNPV C1 was nearly two- to threefold higher at 24 and 48 h post-infection (p.i.) than that of HaSNPV G4. However, the kinetics of polyhedral inclusion body (PIB) formation in HzAM1 cells was similar in both the genotypes, which implied that the insect-killing speed was not influenced by PIB formation, but by the kinetics of BV production. The results suggested that the HaSNPV C1 isolate was a better choice than HaSNPV G4 virus for controlling H. armigera.     

A synchronous peroral technique for the bioassay of insect viruses

A relatively fast and simple peroral technique for the bioassay of insect viruses is described in which newly hatched larvae ingest a uniform volume of virus suspension. Three isolates of the Autographa californica nuclear polyhedrosis virus (NPV) and one isolate of the Heliothis zea NPV were used to test the procedure with Trichoplusia ni and H. zea larvae, respectively. Within-assay and between-assay variation was very low with coefficients of variation averaging 0.012 ± 0.006 and 0.20 ± 0.04 for time-mortality and dose-mortality tests, respectively. The synchronous uptake of virus removed the acquisition-time component of the LT₅₀ values while the constant volume improved the accuracy of LD₅₀ values. The procedure was shown to be suitable for a wide variety of lepidopterous species, including Spodoptera frugiperda, S. eridania, Estigmene acrea, Plutella xylostella, Choristoneura fumiferana, Ostrinia nubilalis, Plodia interpunctella, and Pieris rapae.     

Resistance ofSpodoptera frugiperda [Lep.: Noctuidae] to a nuclear polyhedrosis virus in the field and laboratory

Median lethal doses (LD₅₀s) of nuclear polyhedrosis virus (NPV) were determined in neonatal offspring ofSpodoptera frugiperda (J. E. Smith) (Sf) larvae captured in southeastern Louisiana in 1981, 1982, and 1984. These LD₅₀s ranged from 1.8 to 16.3 polyhedral inclusion bodies (PIB)/insect. The LD₅₀s significantly (P<0.05) increased during the season of 1982 but had no pattern in 1981 or 1984. However, the Sf populations increased in heterogeneity of response to the NPV during all 3 years. The LD₅₀ increased from 4.1 to 18.7 PIB/insect in a Sf laboratory colony exposed to the NPV LD₈₀ for 7 generations, whereas in a control colony not exposed to NPV the LD₅₀ was 5.9 PIB/insect after 7 generations.     

Bioassay of a nuclear-polyhedrosis virus and Bacillus thuringiensis against the American bollworm, Heliothis armigera, in Botswana

Heliothis armigera is a serious pest in Botswana. Preparations of a local nuclear-polyhedrosis virus and Bacillus thuringiensis (Biotrol BTB-183) are being considered as treatments for control of this pest. Laboratory bioassays of these two preparations were carried out to provide a firm basis for comparison with past field trials and a standard for future field testing. The LC₅₀ of the virus and LD₅₀ of B. thuringiensis were found to compare favorably with those for similar materials against closely and distantly related lepidopterous pests. The majority of larvae were killed very rapidly by the B. thuringiensis, although some survived up to 14 days before death. The minimum time to mortality for the virus was 4 days. B. thuringiensis lowered the weight of both male and female surviving pupae, whereas the virus had no significant effect on its survivors. Concentrations of the two materials calculated from the LC₉₀ and LD₉₀ were considerably lower than those already found to give some or good control of H. armigera on sorghum. Improved spray coverage and protection of the materials against environmental degradation are required if spraying concentrations are to be reduced and yet remain effective.     

Comparison of lethalities in mouse versus goldfish for clinical and food isolates ofAeromonas hydrophila

Summary The lethality of 16 clinical or food isolates ofAeromonas hydrophila was assessed by determination of LD₅₀ (i.p.) in mice and goldfish. In mice LD₅₀ values for the variousA. hydrophila strains were similar, ranging from 1.2–21.0×10⁸ cells/animal. A wider range of LD₅₀ values, 0.03–11.8×10⁸ cells/animal, was observed with goldfish. Lethality was not correlated between the two test animals. Further, cytotoxic response in Y-1 adrenal cells did not correlate with lethality in either test animal. It appears that lethality is not a good measure of potential enterotoxigenicity, but may be useful in assessing the invasive character of isolates causing systemic infections in immunocompromised hosts.     

Genetic characterization and fine mapping of the novel Phytophthora resistance gene in a Chinese soybean cultivar

Phytophthora root rot (PRR), caused by Phytophthora sojae Kaufmann & Gerdemann, is one of the most destructive diseases of soybean [Glycine max (L.) Merr.]. Deployment of resistance genes is the most economical and effective way of controlling the disease. The soybean cultivar ‘Yudou 29’ is resistant to many P. sojae isolates in China. The genetic basis of the resistance in ‘Yudou 29’ was elucidated through an inheritance study and molecular mapping. In response to 25 P. sojae isolates, ‘Yudou 29’ displayed a new resistance reaction pattern distinct from those of differentials carrying known Rps genes. A population of 214 F_2:3 families from a cross between ‘Jikedou 2’ (PRR susceptible) and ‘Yudou 29’ was used for Rps gene mapping. The segregation fit a ratio of 1:2:1 for resistance:segregation:susceptibility within this population, indicating that resistance in ‘Yudou 29’ is controlled by a single dominant gene. This gene was temporarily named RpsYD29 and mapped on soybean chromosome 03 (molecular linkage group N; MLG N) flanked by SSR markers SattWM82-50 and Satt1k4b at a genetic distance of 0.5 and 0.2 cM, respectively. Two nucleotide binding site-leucine rich repeat (NBS-LRR) type genes were detected in the 204.8 kb region between SattWM82-50 and Satt1k4b. These two genes showed high similarity to Rps1k in amino acid sequence and could be candidate genes for PRR resistance. Based on the phenotype reactions and the physical position on soybean chromosome 03, RpsYD29 might be a novel allele at, or a novel gene tightly linked to, the Rps1 locus.     

Molecular mapping of leaf rust resistance gene LrFun in Romanian wheat line Fundulea 900

Leaf rust, caused by Puccinia triticina, is one of the major wheat diseases worldwide and poses a constant threat to common wheat (Triticum aestivum L.) production and food security. Results from the F₂ and F_2:3 populations derived from a cross between resistant line Fundulea 900 and susceptible cultivar Thatcher indicated that a single dominant gene, tentatively designated LrFun, conferred resistance to leaf rust. In order to identify other possible genes in Fundulea 900, nine P. triticina pathotypes avirulent on Fundulea 900 were used to inoculate F_2:3 families. The results showed that at least two leaf rust resistance genes were present in Fundulea 900. A total of 1,706 pairs of simple sequence repeat (SSR) primers were used to test the parents and resistant and susceptible bulks. Eight polymorphic markers from chromosome 7BL were used for genotyping the F₂ and F_2:3 populations. LrFun was linked to eight SSR loci on chromosome 7BL. The two closest flanking SSR loci were Xgwm344 and Xwmc70, with genetic distances of 4.4 and 5.7 cM, respectively. At present four leaf rust resistance genes, Lr14a, Lr14b, Lr68 and LrBi16, are located on chromosome 7BL. In a seedling test with 12 P. triticina isolates, the reaction patterns of LrFun were different from those of lines carrying Lr14a, Lr14b and LrBi16. Lr68 is an adult plant resistance gene, and it is different from the seedling resistance gene LrFun. Therefore, we concluded that LrFun is a new leaf rust resistance gene.